Oswald Avery, Colin MacLeod, and Maclyn McCarty show that DNA is the transforming material in cells. They use the observations of Griffith and show the transformation of Streptococcus pneumoniae from an avirulent phenotype to a virulent phenotype is the result of the transfer of DNA from dead smooth organisms to live rough ones. They also show that the transforming principle is destroyed by pancreatic deoxyribonuclease, which hydrolyzes DNA, but is not affected by pancreatic ribonuclease or proteolytic enzymes. Macleod was Avery’s research assistant until 1941. By the time he left, he and Avery suspected that the vital substance in bacterial transformation was DNA. McCarty confirmed their hypothesis.
Oswald T. Avery Collection
Avery, O. T., C. M. Macleod, and M. McCarty. 1944. Studies on the chemical nature of the substance inducing transformation of pneumonococcal types. Induction of transformation by a deoxyribo-nucleic acid fraction isolated from pnuemococcus type III. J. Exp. Med. 79: 137-157. In Microbiology: A Centenary Perspective, edited by Wolfgang K. Joklik, ASM Press. 1999, p.116